Mobile terminals such as mobile phones and personal digital assistants have recently found wide use as the mobile communication system develops. There has been a demand for smaller sizes and improved high-frequency characteristics of inductors in order to reduce the size and increase the performance of these mobile terminals.
To meet such a demand, a coil may be formed perpendicularly to the mounting surface having a size reduced by downsizing, such that the core area of a coiled conductor is larger. This is advantageous in securing Q value (a quality factor). The laminated inductor disclosed in Japanese Patent No. 3058164 having such a structure has been known as a type of inductors. Further, to meet such a demand, the lead-out conductor may have the same width as the coiled conductor, so as to restrain the lead-out conductor from impeding the magnetic flux generated from the coiled conductor. This is advantageous in restraining the decrease in Q value. Still further, no external electrodes may be substantially present on a side surface intersecting the axial direction of the coil, such that the magnetic flux are not largely impeded by an external electrode. This is advantageous in restraining the decrease in Q value. For example, the laminated inductor disclosed in Japanese Patent No. 4019071 is known to have the above features.
With the development of the mobile communication system, electronic instruments which have already been downsized to a portable size are being further downsized to a wearable size that allows integration with human bodies. Accordingly, there has been a demand that inductors should also be further downsized beyond the conventional component size and the Q value should be recovered which has been decreased due to reduction of the core sectional area by the downsizing. Additionally, as the electronic instruments are downsized, there has been a demand for mountability (described later) achieved by reducing the area of the external electrodes that will deteriorate. It is demanded to enhance the positional accuracy and the adhesive strength of the components mounted on a printed circuit board.
Conventional measures to restrain reduction of the Q value of inductors were to restrict, in an inductor component, an internal conductor from blocking a part of the magnetic flux distributed from an opening of the coiled conductor via a side surface thereof to the other opening and reduce the floating capacitance generated by the internal conductor, as in the laminated inductors disclosed in Japanese Patent No. 3058164 and Japanese Patent No. 4019071.
Downsizing of components achieved recently leads to reduction in dimensions inside the component. Within the region influenced by the distributed magnetic flux generated around the coil, there are an external electrode, wiring on a printed circuit board on which components are mounted, and wiring in the printed circuit board (the wiring on the printed circuit board and the wiring in the printed circuit board will be hereinafter collectively referred to as “the wiring of the printed circuit board”). With the conventional techniques, when the external electrode and the wiring of the printed circuit board block the magnetic flux, the inductance (L value) is reduced and the Q value that is proportional to the inductance is also reduced.
The above-described means for restraining the reduction of the Q value restricts the freedom in design of an external electrode. The freedom in design refers to the freedom related to, e.g., the position of the connection between the lead-out conductor and the external electrode, the shape of the external electrode, and the area of the same. More specifically, the means for restraining the reduction of the Q value brings necessity that an external electrode should be formed to have a minimized area on the mounting surface only. Thus, with the conventional technique, it is difficult to design an external electrode for good mountability. Therefore, the mountability of the components cannot be retained.